Conventionally, there is known a variable inductor having a variable inductance in operation. For example, a variable inductor is configured to provide switches connected to ground in multiple positions on a wiring formed in a spiral shape and to change the effective length of the wiring by turning ON or OFF the switches. The inductance of the wiring formed in the spiral shape depends on the total length of the wiring. Thus, the inductance may be arbitrarily changed by changing the positions in which the switches are turned ON (see Chang-Tsung Fu, Chun-Lin Ko, Chien-Nan Kuo, and Ying-Zong, “A 2.4-5.4 GHz Wide Tuning-Range CMOS Reconfigurable Low-Noise Amplifier”, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. 56, No. 12, DECEMBER 2008, for example).
More specifically, the above-described variable inductor is configured to connect one of two input/output terminals of the variable inductor to ground via a switch. Thus, the above inductor may be used as only a shunt inductor, and may be applied to a limited range.